1. Field of the Invention
This invention relates in general to a method and apparatus for inserting address signals in a video signal for a video tape apparatus.
2. Description of the Prior Art
In order to edit video and/or audio signals rapidly and precisely, it has been proposed in the prior art to record an address signal on the magnetic tape in addition to the video and/or audio signal. In this case, as the address signal are provided signals of various codes, but the SMPTE time code signal is recommended as an American National Standard and the EBU time code signal is recommended as a standard code for 625 line/50 field television tape recordings. In the art, the above two time code signals are recorded on a record medium along its longitudinal track and read out of the signals can be achieved at tape speeds from slow to high speed. In the case where the record medium is stopped or transported at very low speeds however, the reproduction of the time code signals becomes impossible. In fact upon editing a video tape by a video tape recorder, it is very advantageous for an editor to be able to choose individual frames presented visually at very low tape speeds but the disadvantages of this method of operation is that the address of a chosen frame cannot be readily known with prior art systems.
The time code signals identify each television frame but the identification of its even or odd field and that of the phase of the burst signal of each television field are impossible. Therefore, precise editing cannot be achieved by the known prior art systems.
In a video tape recorder having a still reproduction mode, in order to obtain an address signal in the still reproduction mode, it has been proposed to convert the synchronizing signal in the vertical blanking period of a television signal to a signal corresponding to an address. For example, Japanese Patent Publication No. 42/4540 filed by Nippon Hoso Kyokai published on Feb. 24, 1967 discloses this method. This Japanese Patent Publication discloses an address signal including frame identification that can be reproduced even in a still reproduction mode but since there is no ordinary synchronizing pulse in the vertical blanking period, a special processing is necessary so as to supply the reproduced address signal to other video tape recorders (VTRs) and a time base corrector.
In these prior art devices since one address signal is recorded for each frame reading errors caused by dropouts or guard band noise during reproduction cannot be prevented.